The present invention pertains to methods and apparatus for removal of solutes and/or contaminants including particles from a supercritical processing solution. More particularly, the invention pertains to methods and apparatus for removing additives and contaminants from supercritical processing solutions via a contaminant removal system that incorporates local recirculation of supercritical solutions during purification.
Supercritical fluids are effective mediums for reagent transport, reaction, and removal of impurities. Supercritical fluids are particularly useful for integrated circuit fabrication, including deposition of thin films and cleaning wafers and circuit devices. The increased importance of quality control, coupled with high throughput requirements in the semiconductor industry in particular, require innovative methods of utilizing this technology. What is lacking in the art are more reliable and practical apparatus and methods of using supercritical fluids.
Conventional methods and apparatus that use supercritical fluids for processing wafers involve batch type non-continuous processing. For example, in a supercritical cleaning apparatus, a wafer is placed into an empty process vessel that is then filled and pressurized with a supercritical solution, typically containing some reactant, precursor, or cleaning agent. When the process is complete, the reactor needs to be flushed to remove excess reactant, precursor, cleaning agent, and any contaminants including dissolved and particulate residue before the vessel can be depressurized and the wafer can be removed. The unreacted additives and/or contaminants may be recovered or otherwise handled downstream using a mechanism separate from the supercritical reactor. However, such methods require large amounts of solvent because the supercritical solution containing the precursor, reactant, cleaning agent, or contaminant must either be completely displaced from the reactor or diluted to a level sufficient to avoid precipitation or deposition of the used or unwanted chemicals on the wafer. Additionally, dilution times can be large and throughput suffers.
What is needed therefore are methods and apparatus that recycle supercritical solvents while removing unused reagents from a supercritical reactor more quickly and with minimal solvent wastage.
The present invention pertains to methods and apparatus for removal of one or more solutes from a supercritical process solution. Solute additives and contaminants are removed from supercritical processing solutions via a contaminant removal system that is either part of the process vessel itself or is part of a local recirculation loop in fluid communication with the process vessel. This invention provides supercritical processing methods and apparatus for the removal of additives and contaminants during circulation so that depressurization and substrate removal can occur without contamination. The removal in some cases, for example cleaning residue, can be done continuously during a process to improve its efficiency. Removal mechanisms may include separation, destruction, conversion of the contaminant to acceptable species, or combinations thereof.
After processing a substrate with the supercritical solution, the solutes are separated from the supercritical solution during recirculation to produce a purified solvent The purified solvent can be recirculated to the process vessel for further use in supercritical processing. The solutes are removed from the solution intact, converted to acceptable by-products, or in some cases are destructively removed from the supercritical solution. The intact solutes (either pure or not) can be recovered for disposal or purified for reuse. Solvent volumes and process times for supercritical processing are reduced because dilutions and flushes of the apparatus are obviated.
Thus, one aspect of the invention is an apparatus for removing one or more solutes from a supercritical solution. Such apparatus may be characterized by the following features: a process vessel configured to treat a workpiece (e.g. a semiconductor wafer) with the supercritical solution; a recirculation loop coupled to the process vessel and allowing fluid communication with the process vessel, and a contaminant removal mechanism for removing the one or more solutes from the supercritical solution to provide a purified solvent. Preferably at least one of the process vessel and the recirculation loop include components of the contaminant removal mechanism. Preferably the purified solvent is a supercritical solvent.
The contaminant removal mechanism of the invention may treat the supercritical solution in one or more ways in order to separate the one or more solutes from the supercritical solution. Preferably, the contaminant removal system includes at least one of an irradiation mechanism, a heating mechanism, a cooling mechanism, a pressurization mechanism, a depressurization mechanism, a chemical addition mechanism, a filtration mechanism, a phase transfer mechanism, and a fluid pumping mechanism.
In a preferred embodiment, the contaminant removal mechanism removes a coarse fraction of the one or more solutes and then a fine fraction of the one or more solutes. The contaminant removal mechanism can include a plurality of individual removal mechanisms. In one example a contaminant removal mechanism of the invention includes a primary removal mechanism and a secondary removal mechanism. The primary mechanism is for removing the bulk (a majority) of the one or more solutes, and the secondary removal mechanism is for further purifying the process fluid by removing smaller amounts of the one or more solutes that remain in the fluid after the first removal mechanism. The first and second removal mechanisms preferably, but not necessarily, contain different separation mechanisms for removal of the one or more solutes. For example, in a particularly preferred embodiment, the first removal mechanism includes a heating mechanism and/or a cooling mechanism, while the second removal mechanism includes an adsorption mechanism. Preferably heating mechanisms of the invention include at least one of internal electrical or heating fluid circulation coils, external electrical or heating fluid circulation coils, a tube in tube heat exchanger, a shell and tube heat exchanger, and a radiative heating mechanism. Preferably cooling mechanisms of the invention include at least one of an internal or external circulated cooling fluid coils, refridgeration coils, and an evaporative cooling mechanism.
As mentioned the purified solvent is preferably, but not necessarily, a supercritical solvent. In the case that the purified solvent is not supercritical, the contaminant removal system may include mechanisms to convert the purified solvent to a supercritical purified solvent.
Another aspect of the invention is a method of removing one or more solutes from a supercritical processing solution. Such methods may be characterized by the following sequence: flowing the supercritical processing solution through a process vessel and a recirculation loop, at least one of the process vessel and the recirculation loop including components of a contaminant removal mechanism; removing at least a portion of the one or more solutes with the contaminant removal mechanism to produce a purified solvent, the purified solvent having a reduced concentration of the one or more solutes; and recirculating the purified solvent through the process vessel and the recirculation loop. Preferably removing at least a portion of the one more contaminants with the contaminant removal mechanism includes exposing the supercritical processing solution to a set of conditions which separate the portion of said one or more solutes from the supercritical processing solution to produce the purified solvent and a contaminant phase. Also preferably, the purified solvent is a supercritical solvent.
Preferably the set of conditions that the supercritical solution is exposed to in the contaminant removal mechanism includes at least one of heating, cooling, irradiation, pressurization, depressurization, chemical addition, adsorption, filtration, oxidation, reduction, precipitation, and combinations thereof. Preferably at least a portion of the contaminant phase is removed from the contaminant removal mechanism during operation.
These and other features and advantages of the present invention will be described in more detail below with reference to the associated drawings.